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Results for “Conjugative transfer of ARGs”

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PubMed2026

Insights into iron-enhanced denitrification coupled with antibiotic resistant genes control in biochar-based biofiltration systems.

In biofiltration (BF) systems, biochar can enhance pollutant removal by promoting biofilm formation. Its abundant pore structure can also sequester antibiotics away from microbial cells, thereby reducing its bioavailability and accumulation of antibiotic resistance genes (ARGs). However, dense biofilms favor horizontal ARG transfer, especially among denitrifying bacteria, which are prone to stress under low influent C/N conditions. In this study, a strategy combining iron minerals was proposed to alleviate the ARG accumulation in BF systems. Compared with magnetite, goethite and siderite released Fe2+ through microbial dissimilatory iron reduction and chemical dissolution respectively, thereby driving iron‑autotrophic denitrification and enhancing the activity of electron‑transfer mediators (cytochrome c and Fe-S proteins). As a result, the level of nitrosative stress was reduced with significant downregulation of related genes (hmp, hcp, norR, and etc.), which was a driving force for conjugative transfer of ARGs. Specifically, the excessive accumulation of tryptophan and shortage of methionine were thus alleviated, which contributed to the regulation of global repressor gene expression and the mitigation of ARG conjugative transfer. With the combination of goethite or siderite in BF systems, the abundance of resistance genome in biofilm exhibited a reduction of 52.68 ± 3.80% and 41.26 ± 4.20%, respectively, which could effectively reduce the environment-ecological risk of antibiotic and ARGs.

Denitrification↗

PubMed2025

Reversing the paradigm: Oxygen-dependent switch of nTiO₂ from promoting to suppressing ARG conjugation.

The environmental spread of antibiotic resistance genes (ARGs) poses a significant public health threat. While nano-titanium dioxide (nTiO2) is known to promote ARG transfer, its role in prevalent anaerobic environments remains poorly understood. Therefore, we comprehensively evaluated the influence of nTiO2 exposure on the plasmid-mediated ARGs conjugation under aerobic/anaerobic conditions. Under aerobic conditions, nTiO2 significantly promoted the ARGs dissemination through both intra-genus (E. coli to E. coli) and inter-genus (E. coli to P. denitrificans) transfer. Reactive oxygen species (ROS) was determined as the decisive factor driving aerobic conjugation, which increased membrane permeability and downregulated conjugative pathways. Addition of ROS scavenger thiourea effectively abolished the stimulatory effect of nTiO₂ on conjugative transfer. However, nTiO2 treatment significantly inhibited conjugative ARG transfer under anaerobic conditions. The dose-dependent inhibition was confirmed in anaerobic denitrification system. Exogenous H2O2 switched the inhibitory effect of nTiO₂ on anaerobic conjugation. Physical barrier formed by nTiO₂ adsorption might contribute to inhibited conjugative transfer of ARGs. Therefore, this study defines the distinct roles of the inhibitory physical effect caused by the adsorption barrier and promotive chemical effect induced by ROS in the nTiO₂-mediated ARG conjugation, which contributes to a deeper understanding of the environmental propagation mechanisms of ARGs under nanomaterial exposure.

Reactive Oxygen Species↗

PubMed2026

Escalation of CTX-M-producing extensively drug-resistant Shigella spp. in Kolkata, India, following the COVID-19 pandemic.

Shigella spp. is recognized by the World Health Organization as a high-priority pathogen due to its global prevalence, unique pathogenic mechanisms, and growing antimicrobial resistance (AMR). Nearly half of all Shigella strains worldwide are now multidrug-resistant (MDR), and the emergence of extensively drug-resistant (XDR) variants-resistant to ciprofloxacin, ceftriaxone, and azithromycin-has severely limited effective treatment options. The present study is based on prospective laboratory surveillance involving 323 Shigella isolates collected during 2021-2023, with pre-COVID-19 pandemic data included from a previously published study solely for historical comparison. The presence of antibiotic resistance genes (ARGs) was investigated, and whole-genome sequencing (WGS) was performed on representative isolates to assess phylogenetic relatedness with global isolates. Approximately 10% of isolates exhibited resistance to third-generation cephalosporins. While only 3% of Shigella isolates carried the blaCTX-M-15 gene from 2013 to 2019, its prevalence increased to 26% by 2022-2023. Among 38 ceftriaxone-resistant S. sonnei isolates, 33 were also resistant to azithromycin, categorizing them as XDR. These isolates showed 48% clonal similarity and high phylogenetic resemblance to the isolates reported from England. Hybrid genome assembly revealed a plasmid harboring both the blaCTX-M-15 and mphA ARGs. Conjugation experiments and plasmid profiling confirmed the plasmid's transferability. We report a rising trend in third-generation cephalosporin resistance among Shigella spp., primarily driven by the spread of extended-spectrum β-lactamase-producing S. flexneri and the emergence of XDR S. sonnei. These findings underscore the urgent need for strengthened national AMR containment strategies and enhanced international surveillance of cephalosporin-resistant Shigella to mitigate this growing public health threat.IMPORTANCEShigella is a leading cause of diarrheal disease globally and has been prioritized by the World Health Organization due to its rapid acquisition of antimicrobial resistance. Our prospective surveillance in Kolkata, India, reveals a worrisome escalation of third-generation cephalosporin resistance over the past decade, primarily associated with the spread of blaCTX-M-15 and the emergence of extensively drug-resistant (XDR) S. sonnei. The detection of plasmids carrying both blaCTX-M-15 and mphA, coupled with evidence of their transferability, highlights the potential for accelerated dissemination of multidrug resistance. When compared with a global data set of international genomes, the Kolkata XDR isolates were found to cluster closely with isolates reported from England. By linking local surveillance with global genomic context, our findings provide critical insights for treatment guidelines, antimicrobial stewardship, and the design of international containment strategies aimed at curbing the rise of cephalosporin- and azithromycin-resistant Shigella.

India↗

PubMed2026

Virus-mediated fate of antimicrobial resistance genes in livestock manure anaerobic digestion.

Antimicrobial resistance (AMR) poses a critical global health challenge, with livestock manure acting as a significant environmental reservoir for antimicrobial resistance genes (ARGs). Anaerobic digestion (AD) is a pivotal process for mitigating ARG dissemination at the livestock-environment-human interface. This study aims to elucidate the global dynamics of ARGs in AD systems, focusing on virus-host interactions and arms race, to identify actionable strategies for AMR control. We analyzed 205 metagenomic (4.5 Tb) and 36 meta-transcriptomic (640 Gb) datasets, including 15 newly generated datasets, revealing that pig manure AD harbors the highest ARG abundance (0.668 ARGs/16S rRNA), while AD systems generally exhibit limited transcriptional activation of ARGs. We constructed a viral dataset for livestock manure AD (GVD_LMAD), comprising 59,316 DNA and 727 RNA viral operational taxonomic units (vOTUs). Virus-host interactions established by CRISPR-Cas spacer, tRNA and homology matches revealed 889 lytic infections of antimicrobial-resistant bacteria (ARB) compared to only 18 ARG transduction events. Further analysis showed that the relative abundance of vOTUs assigned to the reduction role (4.11% ± 3.19%) was substantially higher than that of reproduction (0.72% ± 0.64%) and transduction (0.19% ± 0.30%), demonstrating that, among viral processes, lysis outweighs transduction in contributing to ARG abundance reduction in AD. Furthermore, an antiviral defense system (ADS) catalogue (GADSC_LMAD), derived from 2760 high-quality metagenome-assembled genomes (MAGs) containing 39,307 ADS, with ADS prevalence in ARB (7.8 ± 6.0 per MAG), indicating an intensified virus-host arms race in AD that may shield ARB from phage lysis. The resulting CRISPR-Cas immune network with expressed spacers targets foreign ARG-carrying sequences (primarily plasmids and ICEs), suggesting a mechanism that restricts horizontal gene transfer (HGT) via conjugation and transformation, despite shielding ARB from phage lysis. Collectively, these findings highlight that viral communities significantly contribute to ARG reduction through phage lysis relative to transduction, while the ADS-mediated arms race, despite protecting ARB, constructs a biological firewall that potentially limits HGT of ARGs. This study provides novel insights into virus-host dynamics as a key mechanism for controlling ARG dissemination in AD systems.

Animals↗

PubMed2024

Horizontal plasmid transfer promotes antibiotic resistance in selected bacteria in Chinese frog farms.

The emergence and dissemination of antibiotic resistance genes (ARGs) in the ecosystem are global public health concerns. One Health emphasizes the interconnectivity between different habitats and seeks to optimize animal, human, and environmental health. However, information on the dissemination of antibiotic resistance genes (ARGs) within complex microbiomes in natural habitats is scarce. We investigated the prevalence of antibiotic resistant bacteria (ARB) and the spread of ARGs in intensive bullfrog (Rana catesbeiana) farms in the Shantou area of China. Antibiotic susceptibilities of 361 strains, combined with microbiome analyses, revealed Escherichia coli, Edwardsiella tarda, Citrobacter and Klebsiella sp. as prevalent multidrug resistant bacteria on these farms. Whole genome sequencing of 95 ARB identified 250 large plasmids that harbored a wide range of ARGs. Plasmid sequences and sediment metagenomes revealed an abundance of tetA, sul1, and aph(3″)-Ib ARGs. Notably, antibiotic resistance (against 15 antibiotics) highly correlated with plasmid-borne rather than chromosome-borne ARGs. Based on sequence similarities, most plasmids (62%) fell into 32 distinct groups, indicating a potential for horizontal plasmid transfer (HPT) within the frog farm microbiome. HPT was confirmed in inter- and intra-species conjugation experiments. Furthermore, identical mobile ARGs, flanked by mobile genetic elements (MGEs), were found in different locations on the same plasmid, or on different plasmids residing in the same or different hosts. Our results suggest a synergy between MGEs and HPT to facilitate ARGs dissemination in frog farms. Mining public databases retrieved similar plasmids from different bacterial species found in other environmental niches globally. Our findings underscore the importance of HPT in mediating the spread of ARGs in frog farms and other microbiomes of the ecosystem.

Animals↗

PubMed2026

Farming reshapes the gut resistome, virulome, and mobilome of Cervidae.

The rapid expansion of cervid farming raises concerns about antimicrobial resistance (AMR) dissemination, yet its impact on the Cervidae gut microbiome remains poorly characterized. We integrated 89 newly sequenced fecal metagenomes with 599 publicly available datasets, comprising 285 metagenomes from farmed cervids and 370 from wild cervids, to construct a catalog of 15,494 non-redundant metagenome-assembled genomes (MAGs) representing 2,401 species. Our analysis demonstrates that farming profoundly reshapes the gut microbiome's functional composition. Specifically, farmed cervids exhibited significantly higher relative abundance, diversity, and heterogeneity of antimicrobial resistance genes (ARGs) compared to wild counterparts. We observed a robust synergistic relationship between ARGs, virulence factor genes, and mobile genetic element (MGE)-associated genes, identifying 70 ARG-MGE combinations as evidence of potential horizontal gene transfer. Plasmid profiling further suggested that a subset of ARGs may be associated with conjugative plasmids, with plasmid-associated ARGs being significantly more abundant in farmed than in wild cervids. Virome analyses indicated that bacteriophages, particularly Siphoviridae, may serve as mobile reservoirs for ARGs. Notably, Cervidae shared 268 ARG types with humans, including 23 high-risk genes associated with resistance to clinically important antibiotics (e.g. tetX1, vanRD, and bla-CTX-M-178), with Escherichia coli as a key cross-host carrier. These findings highlight that human-impacted cervid gut microbiomes are significant environmental reservoirs of clinically relevant AMR, underscoring the necessity for enhanced antibiotic stewardship and resistance surveillance in managed wildlife within a One Health framework.

Animals↗

PubMed1976

Effect of glucose starvation on the expression of transferred tsx genes in Escherichia coli K12 zygotes.

Escherichia coli K12 Hfr H Tsxs Strs and F- Pro- Tsxr His- Arg- Strr bacteria were conjugated in the absence of arginine with or without glucose. The efficiency of conjugation, measured by the frequency of Pro+ and His+ recombinants was not affected. Arginine starvation alone did not affect the tsxs gene expression which occurred in all the zygotes which had received the gene. In contrast, argine and glucose starvation allows tsxs expression only in those zygotes in which the donor gene had been integrated in the genome. As the glucose starvation brings on a destabilization of the messenger RNA synthesized by the F- cells in absence of arginine, the results can be interpreted as follows: the transferred tsxs genes are transitorily expressed in all the zygotes at the unintegrated state. After this transient period, only thsoe genes integrated in the chromosomes of the zygotes continue to be expressed.

Arginine↗

PubMed2026

Genomic insights into an optrA-carrying plasmid associated with linezolid resistance in clinical Enterococcus faecalis isolates, Argentina.

The spread of the transferable optrA gene poses an increasing threat to the clinical efficacy of oxazolidinones. Here, we characterized a novel optrA-carrying plasmid, pEfa-optrA-Arg, from a linezolid-resistant Enterococcus faecalis clinical isolate from Argentina. The 68,653-bp conjugative plasmid harbored optrA together with multiple antimicrobial resistance genes and showed high similarity to a plasmid previously identified in a bovine isolate from Switzerland. pEfa-optrA-Arg, or a closely related variant, was also detected in E. faecalis isolates from several Argentinian hospitals, highlighting the role of horizontal gene transfer in the spread of antimicrobial resistance across human and animal reservoirs within the One Health continuum.

Enterococcus faecalis↗

PubMed1978

[New indications for the participation of group P plasmids R in the transfer of chromosomal genes in intergenera crosses].

Use of E. coli strains with phenotypes Rec+ and Rec- asrecipients in intergenera crosses confirmed the supposition put forward by the authors formerly that new chromosomal markers in transconjugantes originated due to Psuedomonas aeruginosa. These chromosomal markers were transferred together with plasmid R conditioning the conjugation, and maintained without being built-into E. coli chromosome. Between the arg+ marker and the plasmid R18 there existed labile physical connection demonstrable only under definite conditions of recombinant selection.

Bacteriophages↗

PubMed1979

Genetic mapping of toxin regulatory mutations in Vibrio cholerae.

We have mapped a regulatory site mediating the hyperproduction of cholera toxin in mutants of Vibrio cholerae strain 569B. Mutations in this locus, called htx, result in the hypertoxinogenic phenotype, as measured by the ganglioside filter assay and immunoradial diffusion. Transposon-facilitated recombination was used to construct improved genetic donors in 569B parental and hypertoxinogenic mutant strains. Subsequent mapping by conjugation indicated that the htx locus was closely linked to the rif, str, and ilv loci of V. cholerae. Analysis of recombinants from these crosses suggested the following gene order: thy str htx rif ilv arg. The close genetic linkage of htx to rif (as high as 98%) resulted in a high comutation frequency of these two loci by nitrosoguanidine mutagenesis. Transfer of the htx mutant locus from a hypertoxinogenic donor to several unrelated Tox+ strains of V. cholerae caused a detectable elevation of toxin production in the recipients. These results suggest that toxin production in diverse strains of V. cholerae is controlled by a common regulatory mechanism in which the htx gene product plays a significant role.

Cholera Toxin↗

PubMed2026

Emergence and persistence of ESBL- and carbapenemase-producing Klebsiella pneumoniae-related species in Barcelona wastewater treatment plants.

The World Health Organization classifies extended-spectrum beta-lactamase (ESBL) and carbapenemase-producing Klebsiella pneumoniae as critical-priority pathogens due to their high incidence, mortality, transmissibility, rapid resistance acquisition, and limited treatment options. Beyond clinical settings, their detection in wastewater treatment plants (WWTPs) provides an opportunity to assess their prevalence, persistence, and circulation within wastewater systems. This study characterized 37 antibiotic-resistant K. pneumoniae-related species strains isolated from two WWTPs in the metropolitan area of Barcelona, analyzing their antimicrobial resistance (AMR) profiles, antimicrobial resistance genes (ARGs), biocide and heavy metal tolerance genes (HMTGs), virulence factor genes (VFGs), biofilm-forming capacity, and conjugation ability. Among them, 70.3% were multidrug-resistant (MDR), and 16.2% were extensively drug-resistant. Whole-genome sequencing revealed diverse ARGs; all strains carried β-lactam resistance genes (14 ESBL and 12 carbapenemase producers), nearly all (96.9%) carried biocide or HMTGs, 64.9% harbored integrases, and all carried VFGs. Core-genome SNP analysis identified closely related strains across sampling periods and treatment stages, suggesting long-term persistence within the wastewater treatment system, despite biological and chemical processes in secondary treatment. Most strains (67.6%) displayed biofilm-forming capacity, and conjugation assays confirmed horizontal gene transfer in five of the seven ESBL-producing strains tested. High-risk clones were predominantly detected in the IFAS secondary treatment stage of the Gavà-Viladecans WWTP. The three strains recovered from the reclaimed water of the Baix Llobregat WWTP were ESBL or carbapenemase producers. Altogether, these results provide genomic and phenotypic evidence of the persistence and circulation of antibiotic-resistant K. pneumoniae-related species within wastewater treatment systems.IMPORTANCEWWTPs are essential for urban sanitation and environmental protection. Understanding how clinically relevant pathogens, such as ESBL and carbapenemase-producing K. pneumoniae-related species strains, behave in these settings may inform public health considerations. Investigating the presence and persistence of high-risk MDR pathogens in WWTPs helps identify circulation of AMR, assess the risk of gene transfer, and evaluate the potential for co-selection with other contaminants. This knowledge supports efforts to improve wastewater treatments, strengthen environmental surveillance, and develop integrated One Health strategies to limit the spread of AMR across human, animal, and environmental sectors.

Wastewater↗

PubMed1976

R factor-mediated polarized chromosomal transfer in Escherichia coli C.

Five transferable drug resistance factors (R factors) with the ability to bring about chromosomal transfer in Escherichia coli C were investigated with respect to the direction and origin of chromosome transfer. They were found to constitute two groups, both with a clockwise direction of transfer. One group has its origin of transfer between arg and pro, and the other group has its origin of transfer between try and man on the E. coli C chromosome. With one R factor in particular, the rapid increase in the production of recombinants was followed by a decrease in numbers as mating was prolonged.

Chromosome Mapping↗

PubMed1978

Isolation and characterization of Hfr strains of Erwinia amylovora.

Hfr strains (Hfr 159 and its derivatives, Hfr 160 and Hfr 161) were constructed from Erwinia amylovora ICPB EA178 by introducing an Escherichia coli F'his+ plasmid and then selecting for integration of F'his+ after treatment with acridine orange. The Hfr strains were relatively stable upon repeated transfers on nonselective media. Interrupted mating experiments and analyses of inheritance of unselected markers showed that his+ is transferred by Hfr 159 as the proximal marker at a relatively high frequency (about 5 x 10(-4) recombinants per input donor cell), followed by ilv+, orn+, arg+, pro+, rbs+, met+, trp+, leu+, ser+, and thr+ (not necessarily in that precise order). The donor strains, previously constructed in E. amylovora by integration of F'lac+ from E. coli transfer cys+ as the proximal marker followed by ser+. Further analysis of one of those earlier donor strains, Hfr99, showed that ser+ is followed by arg+, orn+, met+, pro+, leu+, ilv+, rbs+, his+, trp+, and thr+ (not necessarily in that precise order). Thus, the Hfr strains constructed by integration of F'his+ are different, in terms of origin and direction of transfer, from those derived from integration of F'lac+. The applicability of these Hfr strains to mapping the genes on the E. amylovora chromosome is indicated.

Acridines↗

PubMed1978

F'-plasmid transfer from Escherichia coli to Pseudomonas fluorescens.

Various F' plasmids of Escherichia coli K-12 could be transferred into mutants of the soil strain 6.2, classified herein as a Pseudomonas fluorescens biotype IV. This strain was previously found to receive Flac plasmid (N. Datta and R.W. Hedges, J. Gen Microbiol. 70:453-460, 1972). ilv, leu, met, arg, and his auxotrophs were complemented by plasmids carrying isofunctional genes; trp mutants were not complemented or were very poorly complemented. The frequency of transfer was 10(-5). Subsequent transfer into other P. fluorescens recipients was of the same order of magnitude. Some transconjugants were unable to act as donors, and these did not lose the received information if subcultured on nonselective media. Use of F' plasmids helped to discriminate metabolic blocks in P. fluorescens. In particular, metA, metB, and argH mutants were so distinguished. In addition, F131 plasmid carrying the his operon and a supD mutation could partially relieve the auxotrophy of thr, ilv, and metA13 mutants, suggesting functional expression of E. coli tRNA in P. fluorescens. In P. fluorescens metA Rifr mutants carrying the F110 plasmid, which carried the E. coli metA gene and the E. coli rifs allele, sensitivity to rifampin was found to be dominant at least temporarily over resistance. This suggests interaction of E. coli and P. fluorescens subunits of RNA polymerase. his mutations were also complemented by composite P plasmids containing the his-nif region of Klebsiella pneumoniae (plasmids FN68 and RP41). nif expression could be detected by acetylene reduction in some his+ transconjugants. The frequency of transfer of these P plasmids was 5 X 10(-4).

Arginine↗